>> pete williams in our washington bureau tonight. pete, thanks. and after this sad, depressing day in boston, lester holt, part of our team here, is here tonight with the news of this day. lester? >> brian, this heavy police presence will be a way of life for boston residents for some time to come, but there were thousands of visitors here, participants in the race, they came to be a part and to bear witness to a great sporting event. instead they are filing out of town having beared witness to terror. >> reporter: a runner, a camera strapped to her body with a view of the finish line on the horizon. a view that changes in an instant. it is one of countless images that captured the day, images authorities hope also captured the bombers. >> something just blew up. >> there has to be hundreds, if not thousands, of photographs or videos or observations that were made down at that finish line yesterday. and they're sitting out there amongst everyone that's watching this event this morning. >> i need officers. a secondary device! >> reporter: recording